NAME

DESCRIPTION

Yummy code like your mum used to bake!

RECIPES

Basics

These recipes cover some basic stuff that is worth knowing for Catalyst developers.

Delivering a Custom Error Page

By default, Catalyst will display its own error page whenever it encounters an error in your application. When running under -Debug mode, the error page is a useful screen including the error message and Data::Dump output of the relevant parts of the $c context object. When not in -Debug, users see a simple "Please come back later" screen.

To use a custom error page, use a special end method to short-circuit the error processing. The following is an example; you might want to adjust it further depending on the needs of your application (for example, any calls to fillform will probably need to go into this end method; see Catalyst::Plugin::FillInForm).

You can manually set errors in your code to trigger this page by calling

$c->error( 'You broke me!' );

Disable statistics

Just add this line to your application class if you don't want those nifty statistics in your debug messages.

sub Catalyst::Log::info { }

Enable debug status in the environment

Normally you enable the debugging info by adding the -Debug flag to your use Catalyst statement . However, you can also enable it using environment variable, so you can (for example) get debug info without modifying your application scripts. Just set CATALYST_DEBUG or <MYAPP>_DEBUG to a true value.

Sessions

When you have your users identified, you will want to somehow remember that fact, to save them from having to identify themselves for every single page. One way to do this is to send the username and password parameters in every single page, but that's ugly, and won't work for static pages.

Sessions are a method of saving data related to some transaction, and giving the whole collection a single ID. This ID is then given to the user to return to us on every page they visit while logged in. The usual way to do this is using a browser cookie.

Catalyst uses two types of plugins to represent sessions:

State

A State module is used to keep track of the state of the session between the users browser, and your application.

A common example is the Cookie state module, which sends the browser a cookie containing the session ID. It will use default value for the cookie name and domain, so will "just work" when used.

Store

A Store module is used to hold all the data relating to your session, for example the users ID, or the items for their shopping cart. You can store data in memory (FastMmap), in a file (File) or in a database (DBI).

Authentication magic

If you have included the session modules in your application, the Authentication modules will automagically use your session to save and retrieve the user data for you.

Using a session

Once the session modules are loaded, the session is available as $c->session, and can be writen to and read from as a simple hash reference.

Skipping your VCS's directories

Catalyst uses Module::Pluggable to load Models, Views, and Controllers. Module::Pluggable will scan through all directories and load modules it finds. Sometimes you might want to skip some of these directories, for example when your version control system makes a subdirectory with meta-information in every version-controlled directory. While Catalyst skips subversion and CVS directories already, there are other source control systems. Here is the configuration you need to add their directories to the list to skip.

You can make Catalyst skip these directories using the Catalyst config:

See the Module::Pluggable manual page for more information on except and other options.

Users and Access Control

Most multiuser, and some single-user web applications require that users identify themselves, and the application is often required to define those roles. The recipes below describe some ways of doing this.

Authentication (logging in)

Pass-through login (and other actions)

An easy way of having assorted actions that occur during the processing of a request that are orthogonal to its actual purpose - logins, silent commands etc. Provide actions for these, but when they're required for something else fill e.g. a form variable __login and have a sub begin like so:

Authentication/Authorization

This is done in several steps:

Verification

Getting the user to identify themselves, by giving you some piece of information known only to you and the user. Then you can assume that the user is who they say they are. This is called credential verification.

Authorization

Making sure the user only accesses functions you want them to access. This is done by checking the verified user's data against your internal list of groups, or allowed persons for the current page.

Modules

The Catalyst Authentication system is made up of many interacting modules, to give you the most flexibility possible.

Credential verifiers

A Credential module tables the user input, and passes it to a Store, or some other system, for verification. Typically, a user object is created by either this module or the Store and made accessible by a $c->user call.

User objects

A User object is created by either the storage backend or the credential verifier, and is filled with the retrieved user information.

Examples:

Hash - A simple hash of keys and values.

ACL authorization

ACL stands for Access Control List. The ACL plugin allows you to regulate access on a path-by-path basis, by listing which users, or roles, have access to which paths.

Roles authorization

Authorization by roles is for assigning users to groups, which can then be assigned to ACLs, or just checked when needed.

Logging in

When you have chosen your modules, all you need to do is call the $c->authenticate method. If called with no parameters, it will try to find suitable parameters, such as username and password, or you can pass it these values.

Checking roles

Role checking is done by using the $c->check_user_roles method. This will check using the currently logged-in user (via $c->user). You pass it the name of a role to check, and it returns true if the user is a member.

Using authentication in a testing environment

Ideally, to write tests for authentication/authorization code one would first set up a test database with known data, then use Test::WWW::Mechanize::Catalyst to simulate a user logging in. Unfortunately this can be rather awkward, which is why it's a good thing that the authentication framework is so flexible.

Instead of using a test database, one can simply change the authentication store to something a bit easier to deal with in a testing environment. Additionally, this has the advantage of not modifying one's database, which can be problematic if one forgets to use the testing instead of production database.

More information

Authorization

Introduction

Authorization is the step that comes after authentication. Authentication establishes that the user agent is really representing the user we think it's representing, and then authorization determines what this user is allowed to do.

Role Based Access Control

Under role based access control each user is allowed to perform any number of roles. For example, at a zoo no one but specially trained personnel can enter the moose cage (Mynd you, møøse bites kan be pretty nasti!). For example:

With this action, anyone can just come into the moose cage and feed the moose, which is a very dangerous thing. We need to restrict this action, so that only a qualified moose feeder can perform that action.

The Authorization::Roles plugin lets us perform role based access control checks. Let's load it:

This checks $c->user, and only if the user has all the roles in the list, a true value is returned.

check_roles has a sister method, assert_roles, which throws an exception if any roles are missing.

Some roles that might actually make sense in, say, a forum application:

administrator

moderator

each with a distinct task (system administration versus content administration).

Access Control Lists

Checking for roles all the time can be tedious and error prone.

The Authorization::ACL plugin lets us declare where we'd like checks to be done automatically for us.

For example, we may want to completely block out anyone who isn't a moose_feeder from the entire MooseCage controller:

Zoo->deny_access_unless( "/moose_cage", [qw/moose_feeder/] );

The role list behaves in the same way as check_roles. However, the ACL plugin isn't limited to just interacting with the Roles plugin. We can use a code reference instead. For example, to allow either moose trainers or moose feeders into the moose cage, we can create a more complex check:

When the feed_moose action is accessed the second check will be made. If the user is a moose_feeder, then access will be immediately granted. Otherwise, the next rule in line will be tested - the one checking for a moose_trainer. If this rule is not satisfied, access will be immediately denied.

Rules applied to the same path will be checked in the order they were added.

This action works much like auto, in that it is inherited across namespaces (not like object oriented code). This means that the access_denied action which is nearest to the action which was blocked will be triggered.

If this action does not exist, an error will be thrown, which you can clean up in your end private action instead.

Also, it's important to note that if you restrict access to "/" then end, default, etc. will also be restricted.

MyApp->acl_allow_root_internals;

will create rules that permit access to end, begin, and auto in the root of your app (but not in any other controller).

Models

Models are where application data belongs. Catalyst is extremely flexible with the kind of models that it can use. The recipes here are just the start.

Using existing DBIC (etc.) classes with Catalyst

Many people have existing Model classes that they would like to use with Catalyst (or, conversely, they want to write Catalyst models that can be used outside of Catalyst, e.g. in a cron job). It's trivial to write a simple component in Catalyst that slurps in an outside Model:

DBIx::Class as a Catalyst Model

Create accessors to preload static data once per server instance

When you have data that you want to load just once from the model at startup, instead of for each request, use mk_group_accessors to create accessors and tie them to resultsets in your package that inherits from DBIx::Class::Schema:

Tip

Views

Views pertain to the display of your application. As with models, Catalyst is uncommonly flexible. The recipes below are just a start.

Catalyst::View::TT

One of the first things you probably want to do when starting a new Catalyst application is set up your View. Catalyst doesn't care how you display your data; you can choose to generate HTML, PDF files, or plain text if you wanted.

Most Catalyst applications use a template system to generate their HTML, and though there are several template systems available, Template Toolkit is probably the most popular.

Once again, the Catalyst developers have done all the hard work, and made things easy for the rest of us. Catalyst::View::TT provides the interface to Template Toolkit, and provides Helpers which let us set it up that much more easily.

Creating your View

Catalyst::View::TT provides two different helpers for us to use: TT and TTSite.

TT

This will create lib/MyApp/View/MyView.pm, which is going to be pretty empty to start. However, it sets everything up that you need to get started. You can now define which template you want and forward to your view. For instance:

TTSite

Although the TT helper does create a functional, working view, you may find yourself having to create the same template files and changing the same options every time you create a new application. The TTSite helper saves us even more time by creating the basic templates and setting some common options for us.

Once again, you can use the helper script:

script/myapp_create.pl view TT TTSite

This time, the helper sets several options for us in the generated View.

INCLUDE_PATH defines the directories that Template Toolkit should search for the template files.

PRE_PROCESS is used to process configuration options which are common to every template file.

WRAPPER is a file which is processed with each template, usually used to easily provide a common header and footer for every page.

In addition to setting these options, the TTSite helper also created the template and config files for us! In the 'root' directory, you'll notice two new directories: src and lib.

Several configuration files in root/lib/config are called by PRE_PROCESS.

The files in root/lib/site are the site-wide templates, called by WRAPPER, and display the html framework, control the layout, and provide the templates for the header and footer of your page. Using the template organization provided makes it much easier to standardize pages and make changes when they are (inevitably) needed.

The template files that you will create for your application will go into root/src, and you don't need to worry about putting the the <html> or <head> sections; just put in the content. The WRAPPER will the rest of the page around your template for you.

$c->stash

Of course, having the template system include the header and footer for you isn't all that we want our templates to do. We need to be able to put data into our templates, and have it appear where and how we want it, right? That's where the stash comes in.

In our controllers, we can add data to the stash, and then access it from the template. For instance:

All of the information in your stash is available, by its name/key, in your templates. And your data don't have to be plain, old, boring scalars. You can pass array references and hash references, too.

This allowed us to loop through each item in the arrayref, and display a line for each name that we have.

This is the most basic usage, but Template Toolkit is quite powerful, and allows you to truly keep your presentation logic separate from the rest of your application.

$c->uri_for()

One of my favorite things about Catalyst is the ability to move an application around without having to worry that everything is going to break. One of the areas that used to be a problem was with the http links in your template files. For example, suppose you have an application installed at http://www.domain.com/Calendar. The links point to "/Calendar", "/Calendar/2005", "/Calendar/2005/10", etc. If you move the application to be at http://www.mydomain.com/Tools/Calendar, then all of those links will suddenly break.

That's where $c->uri_for() comes in. This function will merge its parameters with either the base location for the app, or its current namespace. Let's take a look at a couple of examples.

In your template, you can use the following:

<a href="[% c.uri_for('/login') %]">Login Here</a>

Although the parameter starts with a forward slash, this is relative to the application root, not the webserver root. This is important to remember. So, if your application is installed at http://www.domain.com/Calendar, then the link would be http://www.mydomain.com/Calendar/Login. If you move your application to a different domain or path, then that link will still be correct.

Likewise,

<a href="[% c.uri_for('2005','10', '24') %]">October, 24 2005</a>

The first parameter does NOT have a forward slash, and so it will be relative to the current namespace. If the application is installed at http://www.domain.com/Calendar. and if the template is called from MyApp::Controller::Display, then the link would become http://www.domain.com/Calendar/Display/2005/10/24.

If you want to link to a parent uri of your current namespace you can prefix the arguments with multiple '../':

Once again, this allows you to move your application around without having to worry about broken links. But there's something else, as well. Since the links are generated by uri_for, you can use the same template file by several different controllers, and each controller will get the links that its supposed to. Since we believe in Don't Repeat Yourself, this is particularly helpful if you have common elements in your site that you want to keep in one file.

Adding RSS feeds

Adding RSS feeds to your Catalyst applications is simple. We'll see two different approaches here, but the basic premise is that you forward to the normal view action first to get the objects, then handle the output differently.

Using XML::Feed

Assuming we have a view action that populates 'entries' with some DBIx::Class iterator, the code would look something like this:

With this approach you're pretty sure to get something that validates.

Note that for both of the above approaches, you'll need to set the content type like this:

$c->res->content_type('application/rss+xml');

Final words

You could generalize the second variant easily by replacing 'RSS' with a variable, so you can generate Atom feeds with the same code.

Now, go ahead and make RSS feeds for all your stuff. The world *needs* updates on your goldfish!

Forcing the browser to download content

Sometimes you need your application to send content for download. For example, you can generate a comma-separated values (CSV) file for your users to download and import into their spreadsheet program.

Let's say you have an Orders controller which generates a CSV file in the export action (i.e., http://localhost:3000/orders/export):

Note the use of quotes around the filename; this ensures that any spaces in the filename are handled by the browser.

Put this right before calling $c->res->body and your browser will download a file named Important Orders.csv instead of export.

You can also use this to have the browser download content which it normally displays, such as JPEG images or even HTML. Just be sure to set the appropriate content type and disposition.

Controllers

Controllers are the main point of communication between the web server and your application. Here we explore some aspects of how they work.

Action Types

Introduction

A Catalyst application is driven by one or more Controller modules. There are a number of ways that Catalyst can decide which of the methods in your controller modules it should call. Controller methods are also called actions, because they determine how your catalyst application should (re-)act to any given URL. When the application is started up, catalyst looks at all your actions, and decides which URLs they map to.

Type attributes

Each action is a normal method in your controller, except that it has an attribute attached. These can be one of several types.

Assume our Controller module starts with the following package declaration:

package MyApp::Controller::Buckets;

and we are running our application on localhost, port 3000 (the test server default).

Path

A Path attribute also takes an argument, this can be either a relative or an absolute path. A relative path will be relative to the controller namespace, an absolute path will represent an exact matching URL.

When using a Local attribute, no parameters are needed, instead, the name of the action is matched in the URL. The namespaces created by the name of the controller package is always part of the URL.

sub my_handles : Local { .. }

becomes

http://localhost:3000/buckets/my_handles

Global

A Global attribute is similar to a Local attribute, except that the namespace of the controller is ignored, and matching starts at root.

sub my_handles : Global { .. }

becomes

http://localhost:3000/my_handles

Regex

By now you should have figured that a Regex attribute is just what it sounds like. This one takes a regular expression, and matches starting from root. These differ from the rest as they can match multiple URLs.

Last but not least, there is the Private attribute, which allows you to create your own internal actions, which can be forwarded to, but won't be matched as URLs.

sub my_handles : Private { .. }

becomes nothing at all..

Catalyst also predefines some special Private actions, which you can override, these are:

default

The default action will be called, if no other matching action is found. If you don't have one of these in your namespace, or any sub part of your namespace, you'll get an error page instead. If you want to find out where it was the user was trying to go, you can look in the request object using $c->req->path.

sub default :Path { .. }

works for all unknown URLs, in this controller namespace, or every one if put directly into MyApp.pm.

index

The index action is called when someone tries to visit the exact namespace of your controller. If index, default and matching Path actions are defined, then index will be used instead of default and Path.

sub index :Path :Args(0) { .. }

becomes

http://localhost:3000/buckets

begin

The begin action is called at the beginning of every request involving this namespace directly, before other matching actions are called. It can be used to set up variables/data for this particular part of your app. A single begin action is called, its always the one most relevant to the current namespace.

sub begin : Private { .. }

is called once when

http://localhost:3000/bucket/(anything)?

is visited.

end

Like begin, this action is always called for the namespace it is in, after every other action has finished. It is commonly used to forward processing to the View component. A single end action is called, its always the one most relevant to the current namespace.

sub end : Private { .. }

is called once after any actions when

http://localhost:3000/bucket/(anything)?

is visited.

auto

Lastly, the auto action is magic in that every auto action in the chain of paths up to and including the ending namespace, will be called. (In contrast, only one of the begin/end/default actions will be called, the relevant one).

package MyApp::Controller::Root;
sub auto : Private { .. }

and

sub auto : Private { .. }

will both be called when visiting

http://localhost:3000/bucket/(anything)?

A word of warning

You can put root actions in your main MyApp.pm file, but this is deprecated, please put your actions into your Root controller.

Note that adding other actions (i.e. chain endpoints) which operate on a track is simply a matter of adding a new sub to CD::Controller - no code is duplicated, even though there are two different methods of looking up a track.

This technique can be expanded as needed to fulfil your requirements - for example, if you inherit the first action of a chain from a base class, then mixing in a different base class can be used to duplicate an entire URL hierarchy at a different point within your application.

for my $field ($c->req-upload)> loops automatically over all file input fields and gets input names. After that is basic file saving code, just like in single file upload.

Notice: dieing might not be what you want to do, when an error occurs, but it works as an example. A better idea would be to store error $! in $c->stash->{error} and show a custom error template displaying this message.

Forwarding with arguments

Sometimes you want to pass along arguments when forwarding to another action. As of version 5.30, arguments can be passed in the call to forward; in earlier versions, you can manually set the arguments in the Catalyst Request object:

Serving static content

Serving static content in Catalyst used to be somewhat tricky; the use of Catalyst::Plugin::Static::Simple makes everything much easier. This plugin will automatically serve your static content during development, but allows you to easily switch to Apache (or other server) in a production environment.

Introduction to Static::Simple

Static::Simple is a plugin that will help to serve static content for your application. By default, it will serve most types of files, excluding some standard Template Toolkit extensions, out of your root file directory. All files are served by path, so if images/me.jpg is requested, then root/images/me.jpg is found and served.

Usage

Using the plugin is as simple as setting your use line in MyApp.pm to include:

use Catalyst qw/Static::Simple/;

and already files will be served.

Configuring

Static content is best served from a single directory within your root directory. Having many different directories such as root/css and root/images requires more code to manage, because you must separately identify each static directory--if you decide to add a root/js directory, you'll need to change your code to account for it. In contrast, keeping all static directories as subdirectories of a main root/static directory makes things much easier to manage. Here's an example of a typical root directory structure:

When you override include_path, it will not automatically append the normal root path, so you need to add it yourself if you still want it. These will be searched in order given, and the first matching file served.

Static directories

If you want to force some directories to be only static, you can set them using paths relative to the root dir, or regular expressions:

You can also define a different icon for the browser to use instead of favicon.ico by using this in your HTML header:

<link rel="icon" href="/static/myapp.ico" type="image/x-icon" />

Common problems with the Static plugin

The Static plugin makes use of the shared-mime-info package to automatically determine MIME types. This package is notoriously difficult to install, especially on win32 and OS X. For OS X the easiest path might be to install Fink, then use apt-get install shared-mime-info. Restart the server, and everything should be fine.

Make sure you are using the latest version (>= 0.16) for best results. If you are having errors serving CSS files, or if they get served as text/plain instead of text/css, you may have an outdated shared-mime-info version. You may also wish to simply use the following code in your Static controller:

Serving Static Files with Apache

When using Apache, you can bypass Catalyst and any Static plugins/controllers controller by intercepting requests for the root/static path at the server level. All that is required is to define a DocumentRoot and add a separate Location block for your static content. Here is a complete config for this application under mod_perl 1.x:

Caching

Catalyst makes it easy to employ several different types of caching to speed up your applications.

Cache Plugins

There are three wrapper plugins around common CPAN cache modules: Cache::FastMmap, Cache::FileCache, and Cache::Memcached. These can be used to cache the result of slow operations.

The Catalyst Advent Calendar uses the FileCache plugin to cache the rendered XHTML version of the source POD document. This is an ideal application for a cache because the source document changes infrequently but may be viewed many times.

We could actually cache the result forever, but using a value such as 12 hours allows old entries to be automatically expired when they are no longer needed.

Page Caching

Another method of caching is to cache the entire HTML page. While this is traditionally handled by a frontend proxy server like Squid, the Catalyst PageCache plugin makes it trivial to cache the entire output from frequently-used or slow actions.

Many sites have a busy content-filled front page that might look something like this. It probably takes a while to process, and will do the exact same thing for every single user who views the page.

Template Caching

Template Toolkit provides support for caching compiled versions of your templates. To enable this in Catalyst, use the following configuration. TT will cache compiled templates keyed on the file mtime, so changes will still be automatically detected.

Testing

Testing is an integral part of the web application development process. Tests make multi developer teams easier to coordinate, and they help ensure that there are no nasty surprises after upgrades or alterations.

Testing

Catalyst provides a convenient way of testing your application during development and before deployment in a real environment.

Catalyst::Test makes it possible to run the same tests both locally (without an external daemon) and against a remote server via HTTP.

Creating tests

The first line declares how many tests we are going to run, in this case two. The second line tests and loads our application in test mode. The fourth line verifies that our application returns a successful response.

Catalyst::Test exports two functions, request and get. Each can take three different arguments:

A string which is a relative or absolute URI.

request('/my/path');
request('http://www.host.com/my/path');

An instance of URI.

request( URI->new('http://www.host.com/my/path') );

An instance of HTTP::Request.

request( HTTP::Request->new( GET => 'http://www.host.com/my/path') );

request returns an instance of HTTP::Response and get returns the content (body) of the response.